The growing demand for portable electronic devices with power-hungry features has led manufacturers to invest in the highest-capacity batteries. But packing so much energy into a small package can be dangerous, as shown by the recent, massive recalls of Sony lithium-ion batteries for Dell and Apple laptops.
We asked MIT materials scientist and battery expert Yet-Ming Chiang, who cofounded the battery startup A123 Systems of Watertown, MA, what makes designing safe, high-energy batteries so difficult–and whether battery capacity can continue to improve without consumer products spontaneously bursting into flames.
Technology Review: Portable electronic devices have been improving quickly, but batteries haven’t been improving nearly as fast. And now we’ve learned that some of the highest-performing batteries can be dangerous. Why has it been so difficult to design high-capacity, yet safe batteries?
Yet-Ming Chiang: One reason it’s hard is that the chemistries that have been most desirable from the energy density point of view require redundant safety systems. But that often comes at the expense of either lower energy or higher manufacturing cost, because you then add protective components that take up some of the space.
TR: So how can batteries be improved?
YC: There really are two routes to as-high or higher energy systems that are safer and lower cost. One is better control of manufacturing quality. Based on what I’ve read in the press about these two recalls [Dell and Apple], it was a manufacturing problem that resulted in metal particles that created some internal short [circuit] problems. So that is quite simply a manufacturing issue.
The alternative approach is to try to make the chemistries intrinsically safe, or at least safer. People are working on this in many laboratories around the world.
Even [with] the current materials that have been used up until now, the general trend is toward alloys and modified compositions that are safer than what had been used in the past. And then there are the more radical changes in chemistry, such as the phosphate chemistry that you just wrote about [in “Safer Lithium-Ion Batteries”].
TR: But the phosphate-based batteries sacrifice energy storage. Are there materials that promise to both increase capacity and safety? Or are higher-capacity batteries inevitably more dangerous?
YC: It’s not inevitable. Having more electrical energy, you can always think of that as having more energy to dissipate. But the difference in safety of different systems is so chemistry specific, so element specific, that it’s possible to have a higher-energy-density system that is at the same time safer.
As an example, if you look on the negative electrode side, there are some tin- and silicon-based alloys that are being studied that will store more lithium per volume by a considerable margin, but do not appear to be any less safe.
TR: But for that to be of any use, you’ve also got to have the positive electrode with a higher capacity. On that side, are there examples of high-capacity, safe chemistries?
YC: I’m going to be a little cryptic and say that we believe there are. There are definitely materials systems that we are interested in on that side, that we believe can be both higher energy and safer.